/*头部样式*/
body{
    margin: 0;
}
header{
    width: 100%;
    height: 45px;
    background-color: #b52221;
    text-align: center;
    color: #FFF;
    line-height: 45px;
}
ul{
    width: 90%;
    margin: 0 auto 0 auto;
    background: #ccc;
}
ul::after{
    content: "";
    display: block;
    clear: both;
}
ul li{
    list-style-type: none;
    float: left;
}